Due to their adhesion, heat resistance and moisture resistance, epoxy resins have many applications for use as adhesives and paints, and also in the advanced technology field as semiconductor device encapsulants. In particular, liquid epoxy resins have undergone a drastic expansion of their applicable areas in the semiconductor field which is in progress toward smaller feature size and higher operating speed, since they can be adapted to the requirements of ultra-fine complex device design. One of the most developing areas for epoxy resins is the flip chip underfill material.
In the current drive for higher operating speeds and integration density, the chip design targets on low-profile large-size chips. To this end, the conventional capillary flow process in which liquid epoxy resin infiltrates into narrow gaps by utilizing the capillary phenomenon has reached a certain limit. Replacement processes have been proposed, one of which is the no-flow underfill process. In this process, an underfill material is applied to a substrate, a chip is placed on the substrate, and the assembly is heated to achieve conduction between the chip and the substrate and cure of the underfill at the same time.
The no-flow underfill material must have different properties from those of the capillary flow underfill, for example, low volatility and wetting and adherent properties to solder balls. In achieving conduction between the chip and the substrate, the underfill material is heated to an elevated temperature above the melting point of solder balls, typically a temperature of 200° C. or higher. Thus, the underfill material should have a minimum volatile content. In order that a satisfactory interface without imperfections (unfilled or separated) be established between the underfill and solder balls, the underfill is required to exert satisfactory wetting and adherent properties to the molten solder balls. The current capillary flow underfill materials, which are cured at relatively low temperatures after solder bonding, do not possess the low volatility and solder ball wetting, failing to comply with the no-flow process.
With respect to the no-flow underfill, reference should be made to Zhuqing Zhang, Lianhua Fan, C. P. Wong, IEEE Electronic Components and Technology Conference, 2001, p. 1474.